Methods of making a color filter for a liquid crystal display panel or the like include dyeing method, pigment dispersion method, printing method, and electrodeposition method.
In the dyeing method, a photosensitive material is added to the water-soluble polymer material which is the dye material, sensitizing it to light, and after this has been patterned by a lithographic process, it is steeped in a dye solution, to obtain the colored pattern.
For example, first an opaque portion (generally black and referred to as a "black matrix", hereinafter abbreviated to BM) is formed on a glass substrate. Then the dye material, which is made by adding photosensitive material to water-soluble polymer material so that when exposed to light the solubility in a solvent is reduced, is coated on the substrate on which the BM is formed. Next a part only of the dye material is exposed to light through a mask and then developed, thus carrying out patterning so that the dye material remains only in the areas of the first color. Next the dye material is steeped in dye solution to be dyed and then set to form the first color layer. This process is repeated three times, to form a three-color filter.
Whereas a color filter made by the dyeing method has a high transmissivity and bright colors, it is characterized by inferiority with respect to light-resistance, heat-resistance and hygroscopicity.
Next, in the pigment dispersion method, a photosensitive resin in which pigment has been dispersed is coated on a substrate, and this is patterned to obtain a single-color pattern; this process is then repeated. In the above dyeing method, the dyeing is carried out after patterning the dye material, whereas with the pigment dispersion method a photosensitive resin which has already been colored is coated on the substrate. A color filter made by the pigment dispersion method is characterized by high durability, but is somewhat reduced transmissivity.
Furthermore, of the layer of photosensitive resin, at least more than 70% of the amount applied must be removed and disposed of, producing a big problem in the efficiency of use of the material. in the printing method, paint made by dispersing pigment in thermosetting resin is applied by repeated printing to form three colors respectively, and the resin is heat-cured to form the color layer. While the printing method is simple, it is inferior in flatness.
In the electrodeposition method, a patterned transparent electrode is provided on a substrate, and then this is immersed in an electrodeposition fluid containing pigment, resin, electrolyte and so forth, for electrodeposition of the first color. This process is repeated three times, and then finally baking is applied. The electrodeposition method provides excellent flatness, and is effective for color arrangement in a striped pattern, but is difficult to form a color arrangement in a mosaic pattern.
Of the above methods of fabrication, the printing method has a drawback with respect to accuracy, and the electrodeposition method has a drawback of restrictions of patterning, and for this reason conventionally the dyeing method and pigment dispersion method have been most widely used.
However, the dyeing method and the pigment dispersion method require a lithography step for forming the pixel regions of each of the first color, second color and third color, and this is a big obstacle to improve the mass production efficiency of the color filter. One method for forming pixels without a lithography step for each color is an inkjet method of making a color filter, which is disclosed in a number of publications, for example, Japanese Patent Application Laid-Open No. 59-75205 and Japanese Patent Application Laid-Open No. 61-245106. By using an inkjet method to form the pixels, the efficiency of use of material improves, and the process is made shorter, and moreover a color filter of high brightness can be obtained.
One method of thus making a color filter by the inkjet method which has been proposed includes steps of: injecting ink of predetermined colors in a plurality of ink filling. concavities which are formed in a predetermined pattern on a template to form a color pattern layer; then attaching a substrate on the surface of the template on which the color pattern layer is formed with a layer of resin therebetween; thereafter removing the color pattern layer, the resin layer and the substrate as one from the template.
In other words, in this method of making a color filter, the form of the color pattern layer is controlled by the ink filling concavities on the template, and a color filter of high precision can be obtained.
However, in the above described method of making a color filter, there is room for improvement in the following aspects of the step of separating the color pattern layer and resin layer from the template.
Firstly, unless there is good adhesion between the substrate and the resin layer, when the color pattern layer and resin layer are removed as one from the template, the resin layer becomes partially or wholly detached from the substrate, letting the resin layer float above the substrate or break away from the substrate.
Besides, since the adhesion between the color pattern layer and the template is different with each color, separation from the template is not uniform, and transfer faults occurs, such as the color pattern layer breaking away, cracks occurring or deformation.
On the other hand, by making the adhesion between each color pattern layer and the template the same, the detachment from the template can be made uniform, and transfer faults can be avoided, but since the balance with other characteristics required of ink such as the color characteristics and the ejection characteristics of the inkjet method must be considered, the difficulties with the composition and selection of the ink material further increases.
The invention is to solve the above described problems, and its object is to provide a color filter and a method of making the same, such that the process of detachment from the template can be carried out smoothly.